Contamination indicator

ABSTRACT

A contamination indicator for filter elements ( 12 ) for fluids that are replaceably housed in a filter housing ( 2 ), said indicator having a fluid-conveying connection ( 58 ) to the interior of the housing ( 2 ) and possessing an indicating device ( 52 ), which provides information concerning the degree to which the filter element is contaminated ( 12 ), said contamination indicator being characterized in that a temperature-dependently active actuation device ( 50 ) is present, which is connected upstream from the indicating device ( 52 ) in the direction of fluid inlet, by means of which actuation device the indicating device ( 52 ) is activated when the fluid temperature has reached a predefinable threshold value.

The invention relates to a contamination indicator for filter elements for fluids that are replaceably housed in a filter housing, said indicator having a fluid-conveying connection to the interior of the housing and possessing an indicating device, which provides information concerning the degree to which the filter element is contaminated.

Contamination indicators of this type are known in the prior art (DE 101 27 021 C1) and are used in hydraulic systems, in which it is necessary to replace used filter elements located in the fluid circuit with new filter elements once a certain degree of contamination has entered in order to maintain the operational reliability of the system. It is known that the manner in which such contamination indicators function is based on the fact that an increase in pressure in the fluid intake, thus the dirty side in the filtering process, is associated with increasing contamination of the filter element. Accordingly, the manner in which such contamination indicators function is based on the fact that these indicators have a movable element such as a plunger or membrane, which is acted upon by pressure on the dirty side, the deflection of which element provides an indication of the degree to which the filter element is contaminated.

If a hydraulic system is put into operation in a cold state, there is a risk that the indicating device of the contamination indicator will signal a degree of contamination that falls below a threshold value that has been predefined as acceptable. This is due to the fact that the flow resistance of the filter element is a function of the viscosity of the fluid in the hydraulic nil and the viscosity, in turn, is largely a function of the fluid temperature so that in the case of a cold start-up and during the cold phases before reaching the normal operating temperature, which may be in the range of 40° C. for example, the pressure that arises on the dirty side will signal an insufficient degree of contamination.

In view of these problems, the object of the invention is to provide a contamination indicator of the above mentioned type, in which the display errors due to temperature-induced changes in the viscosity of the fluid are minimized.

This object is achieved according to the invention by a contamination indicator having the features of claim 1 in its entirety.

In accordance with the characterizing portion of claim 1, due to the fact that a temperature-dependently active actuation device is connected upstream from the indicating device in the direction of fluid inlet, which actuation device activates the indicating device when the fluid temperature has reached a predefinable threshold value, the indicating device does not generate a signal before reaching the predetermined operating temperature so that the contamination indicator functions as desired, in a temperature-dependent manner.

A differential pressure indicator that detects the pressure differential prevailing in the filter element during operation may be provided as an indicating device, to which indicator the pressure of the clean side of the filter element is supplied as an active component and when the actuation device is active, by means of which indicator the pressure of the dirty side is supplied as a countering active component. The measured value of the pressure differential, which represents the contamination-dependent flow resistance of the filter element, can be optically, electrically or acoustically signaled by means of an indicating device according to the prior art. DE 101 27 021 C1 discloses an example of such a differential pressure indicator device, which generates an electrical measurement signal. A differential pressure indicator from the VD Series sold by Hydac international GmbH can be provided as an optical display, for example the indicator having the product designation VD2 B1 for a response pressure of 0.8 bar.

Alternatively, a back pressure indicator may be provided as an indicating device, to which the pressure of the dirty side of the filter element can be supplied via the active actuation device as an active component that counters the static ambient pressure.

In an especially advantageous manner, the actuation device may have a valve device having a movable closing body, which is pretensioned in a closed position that blocks the fluid inlet to the indicating device, and which can be moved into an open position that releases the fluid inlet by a temperature-dependently active positioning device that is associated with the valve device.

In especially advantageous embodiments, the positioning device provided in order to actuate the actuation device has a expansion element, which, being connected upstream from the closing body in the direction of fluid inlet, comes into contact with fluid, and which is coupled with the closing body in such a way that this closing body can be moved into the open position through the thermal expansion of the expansion element. Due to the fact that the expansion element comes into contact with fluid in such a way, an efficient thermal coupling between the fluid and the expansion element is implemented in the simplest manner. The contamination indicator according to the invention is thereby distinguished by a significantly improved measurement precision as compared to currently available contamination indicators according to the prior art, in which an external thermostat is provided, for example such as that disclosed in DE 66 01 591 U, with the aim of preventing an electric signal from being emitted during cold-start conditions. Since the bimetallic spring of the thermostat in this solution is located outside of the fluid area the display is strongly influenced by the temperature of the surrounding air and accordingly, is inaccurate. Due to the far better thermal connection between the fluid and the expansion element provided in the invention, the precision of the indicating device according to the invention is thus far better.

In an especially advantageous manner, the closing body of the actuation device may be formed by a spool, which is guided in a valve cylinder that forms a part of the fluid inlet, and which can be shifted into the open position by an expansion of the expansion element, in which open position said spool releases an outlet of the valve cylinder that leads to the indicating device, and the pressure signal on the indicating device thereby becomes active.

In advantageous embodiments, an expanding body may be provided as an expansion element in the valve cylinder, which expanding body is supported on one side on the spool and on the other side on an end part of the valve cylinder. Alternatively, a spring formed out of a metal alloy having shape memory may be provided as an expansion element, which spring expands to a greater length upon heating, and which is supported on one side on the spool and on the other side on an end part of the valve cylinder. In both cases, in the case of the mechanical coupling provided according to the invention, a simple, operationally reliable and especially compact design can be implemented between the expansion element and spool for the actuation device.

The configuration may be advantageously such that the valve cylinder of the actuation device is formed in a valve block, in which the indicating device in the form of an insert is housed, and in which inner fluid connections are formed for the respective fluid inlets. The contamination indicator, including the indicating device, and the actuation device, including its temperature-dependent positioning device, are thereby consolidated into a compact assembly in the form of an adapter, which can be affixed to a corresponding filter housing.

To this end, the valve block may advantageously have a connecting port, which can be screwed into a connecting bore of the head section of the appropriate filter housing, and which has at least one inner fluid passage, which, as part of the fluid inlet to the actuation device, forms the fluid-conveying connection to the interior of the filter housing via the connecting bore of the head section.

In a modified embodiment, the valve device of the actuation device has a seat valve, the closing body of which abuts a valve seat under the pretensioning of a closing spring. Because a valve that can close without leaks is provided, increased reliability against an indication error under cold-start conditions is ensured. In the case of other valve designs such as spool valves, there is leakage, albeit a small degree of leakage, which, after a specific period of time, may trigger an indication of contamination. The complete sealing off of the feed to the indicating device also continues during prolonged cold-start phases until the fluid has reached the desired temperature.

In especially advantageous embodiments, the seat valve is disposed in a valve housing, which has a fluid channel in the form of a stepped bore that extends axially through this housing, in which fine steps form the valve seat for a valve ball of the seat valve. This design of the seat valve in the form of a ball valve can be implemented with a valve housing having a small installation size at little expense.

In terms of the design of the valve housing, the configuration may be such that this housing has a connection part on the input side of the stepped bore in order to form a fluid connection to the dirty side of the filter element, wherein a spring formed out of a metal alloy having shape memory is provided as an expansion element in the end section of the bore adjacent to the connection part, which spring expands to a greater length when heated, which is supported on one side on the end piece, and which transmits a dynamic force against this closing force on the valve ball with its other end upon heating.

Further advantageous embodiments of the valve housing are provided in the dependent claims 14 to 16.

In the following, the invention is described in detail on the basis of the embodiments depicted in the drawings. Shown are:

FIG. 1 a longitudinal section of a shortened illustration of a filter housing that is equipped with a contamination indicator according to one embodiment of the invention;

FIG. 2 a longitudinal section of the separately depicted contamination indicator drawn in a larger scale than that used in FIG. 1;

FIG. 3 a longitudinal section similar to that in FIG. 2, which shows a modified embodiment of the actuation device;

FIG. 4 a longitudinal section similar to that in FIGS. 2 and 3, wherein the actuation device corresponds to the embodiment in FIG. 2 and an embodiment of the indicating device that has been modified vis-a-vis the device shown in FIGS. 2 and 3 is shown;

FIG. 5 a longitudinal section similar to that in FIG. 4, wherein the indicating device corresponds to the embodiment in FIG. 4 and the actuation device in the embodiment as depicted in FIG. 3;

FIG. 6 a longitudinal section of a filter housing, in which the contamination indicator in FIG. 3 is incorporated directly in the filter head;

FIG. 7 a horizontal section of the filter housing in the region of the filter head, provided with an adapter in the form of a modified embodiment of the contamination indicator according to the invention;

FIG. 8 a longitudinal section of just the valve housing of the adapter from FIG. 7 that is enlarged as compared to FIG. 7, wherein the valve device is shown in the closed position;

FIG. 9 an illustration corresponding to FIG. 8, which shows the valve device in the open position, and

FIG. 10 a longitudinal section that is enlarged as compared to FIG. 7 of the adapter, which is equipped with a back pressure indicator.

In FIG. 1 a filter housing as a whole is designated as 2, wherein an adapter with a contamination indicator 6 has been attached to the removable filter head 4 of said housing. The filter housing 2 has a circular cylindrical filter bowl 8 with a closed bottom 10. A replaceable filter element 12 can be housed in the bowl 8, which filter element is formed in a known manner and which has a filter material 14 that forms a hollow cylinder, wherein fluid can pass through said filter material from the outside into an inner filter cavity 16 during operation. The filter head 4, which seals the upper, open end of the filter bowl 8 has a connection part 18 that then overlaps the upper opening edge of the bowl 8, with which the head 4 can be connected with the bowl 8 by means of a thread 20, so that the filter head 4 can be removed for inserting and exchanging a filter element 12.

The filter head 4 has ports, which form a fluid inlet 22 and a fluid outlet 24. A fluid passage 26 is connected to the latter, which opens into the inner filter cavity 16 via a connecting port 28. The fluid passage 26 thus forms the clean side in the filter head 4 during the filtering process. A fluid passage 30 that connects to the fluid inlet 22 opens into the chamber 32 located on the exterior of the filter material 14, so that the fluid passage 30 forms the dirty side during the filtering process.

A connecting bore 36 having an inner thread 34 is formed in the upper side of the filter head 4 such that it is coaxial to the longitudinal axis 34. At the bottom of the connecting bore 36, this bore passes from a highly tapered bore end section 40 into the fluid passage 26, which forms the clean side. At approximately half the length of the connecting bore 36, said bore opens into an access channel 42 having a highly tapered canal end section 44. The access channel 42 extends from the connecting bore 36 is at an angle to the fluid passage 30, which forms the dirty side during operation.

The adapter with a contamination indicator 6, which is shown separately in FIG. 2, has a valve block 48, in which an actuation device 50 and an indicating device 52 are integrated in an assembly in the manner of an adapter. On the connection side 54 located at the bottom in the drawing, the valve block 48 has a centrally located connecting port 56, which can be screwed into the connecting bore 36 in the filter head 4. Bores are formed in the valve block 48 in order to form fluid inlets. A bore 58 and 60 extends from each of these in the connecting port 56 parallel to the axis. A transverse bore 62 that is connected to the bore 58, and a transverse bore 64 that is connected to the bore 60 extend in the valve block 48 perpendicular to these bores. A transverse bore 66 extends above the transverse bores 62, 64 and parallel thereto. The outer ends of the bores 58, 62, 64 and 66 are each closed by a conical plug 68. The bore 60 in the connecting port 56 is open at the free end of the connecting port 56. The other bore 58 that extends in the connecting port opens into a transverse channel 70 on the side of the connecting port 56. In the case of a valve block 48 that is screwed into the filter head 4, the bore 58 is in communication with the access channel 42 via the transverse channel 70 on the connecting port 56 and via the end part 44 of the channel. Thus the transverse bore 62 forms the fluid inlet, which regulates the pressure on the dirty side. On the other side, the bore 60 in the connecting port 56 is in communication at the free end thereof with the fluid connection 26 via the bore end 40 of the connecting bore 36, and therefore regulates the pressure an the clean side, which also prevails at the transverse bore that is connected to the bore 60.

The transverse bore 62 opens into a valve cylinder 74 of the actuation device 50 via a junction 72. A valve spool 46 is guided in the valve cylinder 74 such that it can slide, which valve spool blocks an outlet 76 out of the valve cylinder 74 in the case of the spool position shown in FIG. 2. In the closed position shown in FIG. 2, the spool 46, which has an inner bore 78 that allows a passage of fluid, is pretensioned by means of a spring 80 in such a way that said spool rests against a facing end of an expansion body 82, the other end of which is held at an end part 88 of the valve cylinder 74. The outlet 76 of the valve cylinder 74 is in communication with the transverse bore 66, which in turn forms the connection to a plunger side of a plunger 84, which forms the control element of the indicating device 52 and which is pretensioned in an end position by means of a spring 92. The other plunger side of the plunger 84 of the indicating device 52 is in communication with the transverse bore 64 and therefore is subjected to the pressure of the clean side of the filtering process.

In this configuration, the expansion body 82 in the valve cylinder 74, which has been provided as an expansion element, is in contact with the fluid that conveys the pressure of the dirty side via the transverse bore 62, the junction 72 and the bores 78 in the spool 46. The expansion of the expansion body 82, which is dependent on the temperature of the fluid, moves the spool 46 downward against the force of the spring 80 in FIG. 2 when the fluid temperature has reached a predefined threshold value, such that, upon reaching a predefined temperature, the outlet 76 is released and the pressure signal of the dirty side is fed via the transverse bore 66 of the indicating device 52. Since the pressure of the clean side is simultaneously exerted on the plunger 84 of said device through the bore 64, the indicating device 52 functions as a differential pressure indicator.

As mentioned, an indicating device of a known type that provides an optical, electrical or acoustic signal may be used as the indicating device 52 so that there is no need to discuss this in detail here.

The embodiment in FIG. 3 corresponds to the example in FIG. 2, with the exception that the expansion element is not formed by an expansion body 82 but rather, by a spring 86, which is formed out of a metal alloy having shape memory. Such a spring 86 can be formed out of a nickel-titanium-copper alloy in a known manner such that it expands to a greater length upon heating and thus behaves like the expansion body 52. The spring 86 that is clamped between the spool 46 and the end part 88 of the valve cylinder 50 is such a spring, so that the mode of operation of the example in FIG. 3 corresponds to that of the example in FIG. 2. In so doing, the spring 86 is guided onto a pin 90, which is anchored in the end part 88, and which extends coaxially in the valve cylinder 74.

The embodiment in FIG. 4 provides the same design of the actuation device 50 with an expansion body 82 as that in the embodiment in FIG. 2. The difference is that no differential pressure indicator is provided but rather, a back pressure indicator is provided as an indicating device 52, which, in the case of an activated actuation device 50, signals the pressure of the dirty side relative to the static pressure of the environment. For this reason, when the actuation device 50 is active, the plunger 84, which serves as an indicator element, and which is loaded by a spring 92, is only subjected to the pressure of the dirty side via the transverse bore 66. The transverse bore 64 provided in the valve block 48 for the differential pressure indicator in the examples in FIGS. 1 to 3 is omitted here, as is the bore 60 in the connecting port 56.

The embodiment in FIG. 5 corresponds to that in FIG. 4 with the exception that in the case of the actuation device 50, instead of an expansion body 82, an expansion element, in the form of a spring 86 comprising a spring 86 made out of a metal alloy having shape memory, is provided. As in the example in FIG. 4, the indicating device 52 is again designed as a back pressure indicator, which, as in FIG. 4, is screwed into the valve block 48 as a threaded insert by means of a thread 94.

FIG. 6 shows an embodiment in which the contamination indicator 6, which corresponds to the embodiment in FIG. 3, is not designed as an adapter that can be screwed in, but rather, is directly integrated into the filter head 4 of the filter housing 2. The indicating device 50 is in communication with the fluid connection 30 at the fluid inlet 22 via a channel 96 in the filter head 4. A channel 98 connects the indicating device 52 to the fluid passage 26 at the fluid inlet 24.

FIGS. 7 to 10 show a modified embodiment of the actuation device 50 in the form of an adapter having a valve housing 51 having a connection part 53 at one end, with which the housing 51 can be screwed together with the head section 4 of the filter housing 2, wherein the connection part 53 forms a fluid connection 55 to the dirty side 30 of the filter element 12. The valve housing 51 has a fluid channel in the form of a stepped bore 57, which extends from the connection part 53, which is formed by a screw cap, to the outlet end 59 of the valve housing 51 in an axial direction throughout. In the stepped bore 57, a step 61 at the transition to a narrowed section of the bore 63 forms a valve seat for a ball 65, which forms the closing body of a seat valve in the form of a ball valve. The valve ball 65 is pretensioned in the closed position shown in FIGS. 7, 8 and 10 by a closing spring 67, which is located in the bore segment that runs from the valve seat 61 to the outlet end 59, and which is supported at the end facing away from the ball 65 on a hollow adjustment screw 69, which is located in a threaded section 71 on the bore 57 and which enables an adjustment of the pretensioning of the seat valve.

Between the connection part 53 and the narrowed section of the bore 63, the stepped bore 57 has bore section 73 that has an expanded diameter, in which a spring 86 is located as an expansion element, which expands in length upon heating, as is also provided in the embodiments in FIGS. 3, 5 and 6. The spring 86 is supported on one side on the connection part 53 and on the other side on an actuation part 75, which can be moved in the bore section 73. The actuation part 75 has a tappet 77, which extends through the narrowed bore section 63 to the valve ball 65. The actuation part 75 with the tappet 77 has a recess 79 as a fluid passage to the valve ball 65.

FIG. 9 shows the status of the valve when the spring 86 has been heated, wherein the actuation part 75 is moved by the tappet 77 so that the ball 65 is lifted from the valve seat 61. Since the valve ball 75 has an outer diameter that is somewhat smaller than the inner diameter of the adjacent bore section, the fluid path from the fluid connection 55 on the inlet side to the outlet end 59 is free to trigger a corresponding signal. In FIGS. 7 and 10, an indicating device 52 in the form of a back pressure indicator 81 is connected at the outlet end 59 as a screw-on part, as is also the case in the embodiments in FIGS. 4 and 5. It shall be understood that, as is the case with the embodiments in FIGS. 1, 2 and 6, a differential pressure indicator could likewise be provided, wherein as in the above mentioned embodiments, a differential pressure connection to the clean side of the filter element 12 would be provided.

While the embodiment in FIGS. 7 to 10 is designed as an adapter that can be screwed on, the installation could be provided in the filter head 4, as is shown accordingly for the embodiment in FIG. 6. In addition to its function as a contamination indicator, or alternatively thereto, the invention may also be provided as a protection device in order to protect pressure sensors or other pressure-sensitive devices from an overload in the case of a cold start. 

1. A contamination indicator for filter elements (12) for fluids that are replaceably housed in a filter housing (2), said indicator having a fluid-conveying connection (58) to the interior of the housing (2) and possessing an indicating device (52), which provides information concerning the degree to which the filter element is contaminated (12), characterized in that, a temperature-dependently active actuation device (50) is present, which is connected upstream from the indicating device (52) in the direction of fluid inlet, by means of which actuation device the indicating device (52) is activated when the fluid temperature has reached a predefinable threshold value.
 2. The contamination indicator according to claim 1, characterized in that a differential pressure indicator (52) that detects the pressure differential that prevails at the filter element (12) during operation is provided as an indicating device, to which indicator the pressure of the clean side (16, 26) of the filter element (12) is supplied as an active component and, when the actuation device (50) is active, by means of which actuator, the pressure of the dirty side (30, 32) is supplied as a countering active component.
 3. The contamination indicator according to claim 1, characterized in that a back pressure indicator (52) is provided as an indicating device, to which the pressure of the dirty side (30, 32) of the filter element (12) is supplied, via the active actuation device (50), as an active component that counters the static ambient pressure.
 4. The contamination indicator according to claim 1, characterized in that the actuation device (50) has a valve device (74) having a movable closing body (46), which is pretensioned in a closed position that blocks the fluid inlet (76) to the indicating device (52), and which can be moved into an open position that opens the fluid inlet (76) by a temperature-dependently active positioning device (82; 86) associated with the valve device (74).
 5. The contamination indicator according to claim 1, characterized in that the positioning device has an expansion element (82; 86), which is connected upstream from the closing body (46) in the direction of fluid inlet, comes into contact with fluid, and is coupled with the closing body (46) in such a way that this closing body can be moved into the open position through the thermal expansion of the expansion element (82; 86).
 6. The contamination indicator according to claim 1, characterized in that an expanding body (82) is provided as an expansion element, which expanding body is supported on one side on the closing body (46) and on the other side, on a stationary part (88) of the valve device (74).
 7. The contamination indicator according to claim 1, characterized in that a spring (86) formed out of a metal alloy having shape memory is provided as an expansion element, which spring extends to a greater length upon heating, and which is supported on the one side on the closing body (46), and on the other side, on a stationary part of the valve device (74).
 8. The contamination indicator according to claim 1, characterized in that the closing body is formed by a valve spool (46), which is guided in a valve cylinder (74) that forms a part of the fluid inlet, and which is shifted into the open position by an expansion of the expansion element (82; 86), in which open position said spool releases an outlet (76) of the valve cylinder (74) that leads to the indicating device (52).
 9. The contamination indicator according to claim 1, characterized in that the valve cylinder (74) of the actuation device (50) is formed in a valve block (48), in which the indicating device (52) in the form of an insert is housed, and in which inner fluid connections (58, 60, 62, 64, 66, 76) are formed for respective fluid inlets.
 10. The contamination indicator according to claim 1, characterized in that the valve block (48) has a connecting port (56), which can be screwed into a connecting bore (36) of the head section (4) of the filter housing (2), and which has at least one inner fluid passage (58, 60), which, as part of the fluid inlet to the actuation device (50), forms the fluid-conveying connection to the interior of the filter housing (2) via the connecting bore (36) of the head section (4).
 11. The contamination indicator according to claim 1, characterized in that the valve device (51) of the actuation device (50) has a seat valve (61, 65), the closing body (65) of which abuts a valve seat (61) under the pretensioning of a closing spring (67).
 12. The contamination indicator according to claim 1, characterized in that the seat valve (61, 65) is disposed in a valve housing (51), which has a fluid passage in the form of a stepped bore (57) that extends axially through said housing, on which a step (61) forms the valve seat for a valve ball (65) of the seat valve (61, 65).
 13. The contamination indicator according to claim 1, characterized in that the valve housing (51) has a connection part (53) on the inlet side of the stepped bore (57) in order to form a fluid connection (55) to the dirty side (30) of the filter element (12), and in that a spring (86) formed out of a metal alloy having shape memory is provided as an expansion element in the end section of the bore (57) adjacent to the connection part (53), which spring extends to a greater length upon heating, is supported with one end on the connection part (53), and which transmits a dynamic force against this closing force (67) on the valve ball with its other end (65) upon heating.
 14. The contamination indicator according to claim 1, characterized in that the stepped bore (57) has a narrowed section (63) between the valve seat (61) and the spring (86) that forms the expansion element, through which narrowed section a tappet (77) passes, the end of which abuts the valve ball (65), which tappet has an actuation part (75) on which the spring (86) that forms the expansion element is supported.
 15. The contamination indicator according to claim 1, characterized in that the spring (86) that is serving as an expansion element is located in a bore segment (73) that is widened as compared to the narrowed bore segment adjacent to the valve seat, in which widened bore segment the actuation part (75) having the tappet (77) is movably guided.
 16. The contamination indicator according to claim 1, characterized in that a closing spring in the form of a compression spring (67) is disposed in the bore section that runs from the valve seat (61) to the outlet end (59) of the valve housing (51), in which a threaded section (71) for a hollow adjustment screw (69) is formed, one end of which rests in the closing spring (67), the other end of which is supported on the valve ball (65). 